1. Field of the Invention
The present invention relates to a flat coreless vibrator motor having no output shaft, which motor is suitable used as a silent information source for a small-sized radio calling device (or a pager) or as a vibration source for a massager and, more particularly, to an improved fixed shaft type structure of the coreless vibrator motor provided with a thin fixed shaft.
2. Description of the Related Art
Conventionally, a flat vibrator motor without an output shaft has been known, especially as a flat coreless motor disclosed in the U.S. Pat. No. 5,036,239. As shown in FIG. 6, this motor has the structure wherein a rotor R is eccentrically disposed within a housing H comprised of a casing 28 and a bracket 29 and rotatably supported by a lubricant-containing bearing 32 and 33 disposed in the casing 28 and the bracket 29, respectively, through a rotor holder 30 and a shaft 31. It should be noted that since the eccentric rotor R is fixed to the shaft 31, the position of the rotor R is determined by the shaft 31 which is flush with the housing H.
However, where the motor is of the above-described twin bearing type, the concentricity between the upper and the lower bearings becomes important. In the case of a coin type flat motor whose thickness is about 3 mm, in order to prevent the tilting and blocking of the rotor, it becomes necessary to make the concentricity between the bracket fitting portion and each of the bearings as small as 10 .mu.m or less, so that each of the parts of the motor is required to have a high degree of dimensional accuracy.
Such a problem ought to be solved by using only one of the bearings as a cantilever type bearing, however, as will be understood from the thickness of the motor, the soft lubricant-containing bearing is not practical in use because of the weakness of its fixing strength. When the bearing fitting portion is elongated, the thickness of the motor can not be reduced. When the thickness is forced to be reduced, in turn, the fitting allowance of the rotor holder fitted about the shaft becomes short, resulting in another problem in the actual use thereof.
Further, there is also disclosed in JP-B-59-14966 (refer to FIG. 1) a shaft-fixed type vibrator motor in which the shaft is prevented from projecting outside its housing.
As maybe understood from its drawings, however, since both ends of the shaft are fixed to a bracket, it is difficult to assemble the rotor. That is, to explain the structure by using the reference numerals given in the drawings, it is generally difficult to mount the rotor 12 to the bearings 5 and 6 respectively fitted in the brackets 2 and 3 through the shaft supporting brackets 10 and 11, because of the existence of the stator 7 as an obstacle. Further, the bearings 5 and 6 are not to be mounted to the shaft 4 but unavoidably mounted to the brackets 2 and 3 for the purpose of facilitating the lead wire connection process. Thus, the outer diameter of the bracket is obliged to be made large, so that the sliding loss with respect to the shaft-supporting brackets 10 and 11 becomes too large for the motor to be put in practical use. Unlike the shaft, the degree of roughness of the brackets 10 and 11 cannot be made small.
In this connection, in order to overcome the above-described various problems, the present inventors formerly proposed an invention disclosed in JP-B-6-81443 by taking notice of the fact that a vibrator motor having no output shaft which makes use of the vibration of its rotor itself is not required to rotate its shaft and that the shaft has only to be fixed at one end thereof. Thus, this motor has now been produced as a shaft-fixed type flat vibrator motor having no output shaft. Such a motor is now popular in the market due to the ease of assembly of the rotor and the excellence of its cost performance.
With the recent trend of miniaturization of portable equipment, the motor to be mounted in the equipment is required to be more and more miniaturized with minimum power consumption. If a motor with a shaft having a diameter of about 0.6 mm (a shaft having a diameter of 1.2 mm might be accepted) must be used, such a small-diameter shaft of cantilever supporting type may require careful consideration to its impact resistance making the fixing portion of the shaft large, in turn, may affect adversely the reduction of the overall thickness of the motor.
The present invention has been made to overcome the above-described problems and an object of the invention is to provide a flat vibrator motor having no output shaft with a sufficient degree of impact resistant, using a small-diameter shaft, which can be assembled in a simple manner and which is thereby advantageous in view of manufacturing cost.